Kendall, try this...sometimes when filling a gap its easier to use a bigger rod , it has more metal in it, but try to use it at the same heat setting your using now..just go up one rod size. like the other guys said, use short tacks and let em cool inbetween, the go over it again. the main thing to do is keep the arc as close and short as possible. Once its welded , grind it down smooth, cut a shallow V into it then reweld with the smaller rod at the same setting to be sure of good penetration. Im not sure if you can understand what Im saying, its often easier to show someone. <img border="0" title="" alt="[Big Grin]" src="images/icons/grin.gif" />
Heres another way to try it..take another rod while welding and put it in the arc , it will melt and help fill, sort of like you would do when braising, cept your using an arc instead of a torch...Always to remember to regrind with a shallow V and to reweld a nice bead with good penetration...I hope you understand all this,Dave

BTW if all else fails, put a doubler plate inside it to cover the gap and weld away...